Industrial reactions heterogeneous catalytic, kinetics

The Kinetics of Some Industrial Heterogeneous Catalytic Reactions M. 1. Temkin... 

This chapter presents an account of the main results of studies of kinetics of some industrial heterogeneous catalytic reactions. The studies have been carried out by the author with his co-workers at the Karpov Institute of Physical Chemistry (Moscow, USSR). The presentation is not chronological the reactions are arranged based on the character of interpretation of their kinetics. 

M.I. Temkin, The Kinetics of Some Industrial Heterogeneous Catalytic Reactions in Advances in Catalysis, Vol. 28, Academic Press, New York, 1979, p. 173. 

Temkin, M. 1., The kinetics of some industrial heterogeneous catalytic reactions. Adc. Catal. 26. 173-291 (1979). 

The rate at which a reaction proceeds is governed by the principles of chemical kinetics, which is one of the major topics of this book. Chenucal kinetics allows us to understand how reaction rates depend on variables such as concentration, temperature, and pressure. Kinetics provides a basis for manipulating these variables to increase the rate of a desired reaction, and minimize the rates of undesired reactions. We will study kinetics first from a rather empirical standpoint, and lat from a more fundamental point of view, one that creates a link with the details of the reaction chenustry. Catalysis is an extremely important tool within the domain of chemical kinetics. For example, catalysts are required to ensure that blood clots form fast enough to fight serious blood loss. Approximately 90% of the chemical processes that are carried out industrially involve the use of some kind of catalyst in order to increase the rate(s) of the desired reaction(s). Unfortunately, the behavior of heterogeneous catalysts can be significantly and negatively influenced by the rates of heat and mass transfer to and from the sites in the catalyst whrae the reaction occurs. We will approach the interactions between catalytic kinetics and heat and mass transport conceptually and qualitatively at first, and then take them head-on later in the book. 

Various experimental methods to evaluate the kinetics of flow processes existed even in the last centuty. They developed gradually with the expansion of the petrochemical industry. In the 1940s, conversion versus residence time measurement in tubular reactors was the basic tool for rate evaluations. In the 1950s, differential reactor experiments became popular. Only in the 1960s did the use of Continuous-flow Stirred Tank Reactors (CSTRs) start to spread for kinetic studies. A large variety of CSTRs was used to study heterogeneous (contact) catalytic reactions. These included spinning basket CSTRs as well as many kinds of fixed bed reactors with external or internal recycle pumps (Jankowski 1978, Berty 1984.)... 

Chapter 10 begins a more detailed treatment of heterogeneous reactors. This chapter continues the use of pseudohomogeneous models for steady-state, packed-bed reactors, but derives expressions for the reaction rate that reflect the underlying kinetics of surface-catalyzed reactions. The kinetic models are site-competition models that apply to a variety of catalytic systems, including the enzymatic reactions treated in Chapter 12. Here in Chapter 10, the example system is a solid-catalyzed gas reaction that is typical of the traditional chemical industry. A few important examples are listed here ... 

In heterogeneous catalysis reactants have to be transported to the catalyst and (if the catalyst is a porous, solid particle) also through the pores of the particle to the active material. In this case all kinds of transport resistance s may play a role, which prevent the catalyst from being fully effective in its industrial application. Furthermore, because appreciable heat effects accompany most reactions, heat has to be removed from the particle or supplied to it in order to keep it in the appropriate temperature range (where the catalyst is really fully effective). Furthermore, heterogeneous catalysis is one of the most complex branches of chemical kinetics. Rarely do we know the compositions, properties or concentrations of the reaction intermediates that exist on the surfaces covered with the catalytically effective material. TTie chemical factors that govern reaction rates under these conditions are less well known than in homogeneous catalysis. Yet solid catalysts display specificities for particular reactions, and selectivity s for desired products, that in most practical cases cannot be equaled in other ways. Thus use of solid catalysts and the proper (mathematical) tools to describe their performance are essential. 

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